Problem: Convert the angle 90° to radians.
There are $360$ degrees in a circle. There are also $2\pi$ radians in a circle. In other words, there are $\pi$ radians per $180$ degrees. So we can convert from degrees to radians by multiplying by $\pi$ , and dividing by $180^\circ$ $ 90^\circ \times \dfrac{\pi}{180^\circ} $ $ = \frac{\pi}{2}$ radians